Genetic Type of Natural Gas of Marine Facies in Jiannan Gas Field
WANG Shao-hua, WANG Yu-qiang, LING Zhuan-hua (China University of Geosciences, Wuhan 430074, Hubei, China; Exploration & Development Research Institute, Jianghan Oilfield Company, SINOPEC, Qianjiang 433124, Hubei, China)
There were four gas-bearing strata with commercial value in Jiannan Gas Field, including Jia-1 Member, Fei-3 Member, Changxin Member and Huanglong Member. The gas in these reservoirs sourced from the lower Triassic, Permian and the Lower Silurian. Through studying the component of natural gases and carbonic isotope characteristics of alkanes from different gas-bearing strata and component of light hydrocarbon, it is believed that those natural gases are pyrolysis gases formed under high temperature as organic origin. The carbon isotopes of methane and ethane are generally inversed in Jiannan Gas Field, mainly come from mixture of coal-derived and oil-derived gases in source rocks with different maturities. Mixed gases in natural gas reservoir are mainly contributed to oil-derived gases. Genetic type of natural gas in carbonate mainly belongs to water-dissolved gases of oil-separated gases from Silurian hydrocarbon source rocks.